There are six principal process methods of applying thermally
sprayed coatings to engineered parts and structures, namely:
- High Velocity Oxygen / Fuel Process,
- Low Velocity Oxygen / Fuel Process,
- Flame Sprayed Hardfacing,
- Plasma Flame Process,
- Electric Arc Wire Metallising,
- Combustion Arc Wire Metallising.
Although differing substantially in the type of equipment
used, these processes share the common features of being 'cold
processes', in that little heat is transferred to the workpiece,
and can spray materials that exhibit a liquid phase when heated.
Thus high melting point refractory metals and ceramics such
as molybdenum and zirconia can be thermally sprayed whereas,
for example, silicon carbide ceramic which 'sublimes' from a
solid to gas phase when heated, and wood which converts to charcoal,
cannot be thermally sprayed.
Given this exception, all materials from aluminium to zinc
including carbides, ceramics and thermoplastics are capable of
being thermally sprayed to give coatings of wear resistance,
corrosion resistance, thermal barrier heat resistance and sacrificial
surface abradability. The properties of Flame
Sprayed Hardfacing coatings are enhanced by high temperature
heat treatment which promotes bond strength and increases coating
hard wearing properties.
Principle areas of use include the following:
- Aero, land and marine gas turbine manufacture, repair and
overhaul.
- The corrosion proofing of steel structures such as bridges
and oil rigs.
- Chemical process plant.
- Pump impeller wear rings and seal sleeves.
- Yarn thread guides.
- Automotive engine parts.
- Quarry plant stone processing parts.
- Steel rolling mill work rolls and components.
- Domestic and chefs' kitchen knives.
Coating environment, duty requirements and cost effectiveness
dictate the type of coating selected and the process used to
deposit it.
